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Date:   Thu, 4 Apr 2019 16:33:27 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Vince Weaver <vincent.weaver@maine.edu>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jiri Olsa <jolsa@redhat.com>,
        Stephane Eranian <eranian@google.com>
Subject: Re: perf: perf_fuzzer crashes on Pentium 4 systems
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On Thu, Apr 04, 2019 at 09:25:47AM -0400, Vince Weaver wrote:
> 
> It looks like there are at least two bugs here, one that's a full 
> hardlockup with nothing on serial console.  The other is the NULL 
> dereference.
> 

Seems so. I've spent plenty of time yesterday trying to figure out how
we even reach the case when event = nil but without much luck.

> Just ran with your patch applied and it hit the hard lockup case.
> 
> I'll have to see if things are reproducible and I can try to see if I can 
> get a reproducible value for what even caused the issue.  perf_fuzzer has 
> some infrastructure for determining that but it's hit or miss if you can 
> get anything useful from it.

At least the sequence of events migh give us some ideas, maybe not indeed.
Thanks a huge, Vince!

> I'll keep running things, but I'm a bit busy at work here the next few 
> days so there might be some delay in the results.

Sure, take your time. I think this problem with p4 is not urgent. I'll ping
you if I get some more ideas.